Power Amplifier Bias Circuit for Multi-Mode Linearity Control
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Solution Overview
Problem
Power amplifier modules in mobile communication devices face challenges in maintaining high linearity across varying operation modes, particularly with wide dynamic ranges, which affects power consumption and efficiency.
Innovation Solution
A power amplifier module with a bias circuit that includes first and second transistors and resistors, where the transistors are turned ON/OFF based on specific bias control voltages to supply optimal bias current depending on the operation mode, enabling suitable bias control for multiple operation modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high power supply voltage is used to maintain high linearity in a wide dynamic range, then linearity is improved, but power consumption increases
Solution Approach 1:
The power supply voltage is made dynamic by adjusting it in accordance with the amplitude level of the input modulation signal through envelope tracking. This allows the voltage to vary over time to match the signal requirements, maintaining high linearity when needed while reducing power consumption during low-power periods.
Solution Approach 2:
The power supply voltage parameter is changed dynamically based on the signal amplitude level. By varying this parameter in real-time through envelope tracking, the system achieves high linearity when the signal requires it while consuming less power during low-amplitude periods.
2Loss of energy
If envelope tracking is used to improve power efficiency, then power-added efficiency is improved under high power, but linearity control becomes complex across different operation modes
Solution Approach 1:
The bias control is segmented into multiple independent circuits, each dedicated to a specific operation mode (e.g., one circuit for envelope tracking mode, another for average power tracking mode). This segmentation allows each circuit to be optimized for its specific mode without interfering with others, simplifying the overall control complexity while maintaining power efficiency.
Solution Approach 2:
The bias control system is designed with multi-functionality by incorporating multiple bias control circuits that can handle different operation modes. Each circuit serves a specific function for a specific mode, but collectively they provide universal coverage for all operation modes, enabling the system to maintain power efficiency across diverse operating conditions.
3Device complexity
If a single bias control circuit is used for all operation modes, then device complexity is reduced, but optimal bias control for all modes cannot be achieved
Solution Approach 1:
The bias control system is divided into multiple independent circuits, each optimized for a specific operation mode. This segmentation ensures that each circuit can provide optimal bias control for its designated mode, thereby improving overall reliability and performance across all operation modes despite increased circuit count.
Data Source
AI summary
A power amplifier module includes an amplifier transistor and a bias circuit. A first power supply voltage based on a first operation mode or a second power supply voltage based on a second operation mode is supplied to the amplifier transistor. The amplifier transistor receives a first signal and outputs a second signal obtained by amplifying the first signal. The bias circuit supplies a bias current to the amplifier transistor. The bias circuit includes first and second resistors and first and second transistors. The first transistor is connected in series with the first resistor and is turned ON by a first bias control voltage which is supplied when the first operation mode is used. The second transistor is connected in series with the second resistor and is turned ON by a second bias control voltage which is supplied when the second operation mode is used.